Nor do I think it makes sense that there's such a vast difference in numbers from Lanfear to Graendal.

While Lanfear strength women are surely rarer than Graendal strength women, they cannot be that much rarer given the bell curve distribution. As we move towards the upper echelons (and the lower) the curve is getting flatter, and closer to zero.

Its more likely one in 100,000 for Lanfear, 1 in 95,000 for Grandal and 1 in 90,000 for Nynaeve (assuming the old list is still true).